Kitkoan wrote on Oct 30, 2012, 00:43:Last I knew, the BSD is GPL. And thats why Darwin is "open source" because its the part Apple legally needs to keep open. Everything else they tack on to it on the other hand isn't GPL.

So Apple is using the base engine and keeping it as open as needed, every little modification and screw change they do, they don't open up because they don't need to legal. The GPL doesn't cover that